The present invention relates to a new and improved absorbent structure which may be used in a disposable absorbent article having a fast liquid penetration rate and high liquid retention, and which allows the skin of a wearer to remain dry even after the article has become wet.
Disposable absorbent articles have long been used to absorb body exudates to prevent staining or soiling of a wearer's clothing. Examples of such articles include feminine sanitary napkins, diapers, and adult incontinence products. Initially, such articles had absorbent cores constructed primarily of traditional cellulosic fiber materials, such as tissue wadding and/or wood pulp fluff. These cellulosic fiber materials demonstrate good dry resilience and good absorbency for body fluids. However, once cellulosic fiber materials become wet, they tend to "collapse" and lose their resilience. In other words, the wet cellulosic fibers become limp and compacted together, thereby causing the structure to lose the fluid-holding benefit of the spaces between the fibers. Furthermore, such wet cellulosic fiber materials are unable to absorb further additions of fluid, otherwise known as repeat fluid insults. Wet cellulosic fiber products also provide an unpleasant wet, soggy feeling against a wearer's skin.
More recently, superabsorbent particles have been added to cellulosic fiber materials in disposable absorbent articles to improve their absorbent capacity and to provide the articles with a drier feel against a wearer's skin. Although superabsorbent particles do not collapse when wet, they do not absorb fluid as rapidly as cellulosic fiber materials. Large volumes of fluid added rapidly to a superabsorbent material will tend to run off if not held in fluid contact with the superabsorbent for some time. Therefore, it has also become common to use so-called transfer layers between the absorbent core and the body-facing surface of the article. Transfer layers are generally resilient fibrous webs which provide void volume for rapidly taking up fluid and then releasing it more slowly to the adjacent absorbent core to allow time for the superabsorbent materials to absorb the fluid. Transfer layers also provide an insulating layer between the absorbent core and the wearer, preventing contact between a wet absorbent core and the wearer's skin. Such transfer layers are somewhat limited, however, since their fluid-transporting effectiveness depends upon their intimate contact with the underlying absorbent core. Therefore, the article must be constructed such that the transfer layer remains in good contact with the absorbent core during wearing conditions. The inherent void volume of the transfer layer, and thus its liquid-holding capacity, is limited by its thickness; i.e., a thicker transfer layer provides greater void volume, but if it is too thick, it becomes bulky and therefore, uncomfortable and indiscreet to the wearer. Therefore, thin transfer layers are preferred for wearer comfort, but their small void volume allows them to hold only a small volume of fluid.
The object of this invention is to provide an absorbent structure with a fast fluid penetration rate for initial fluid add-on and for repeat fluid insults, good wet and dry resilience, and good surface dryness.